Laticifers in the leaves and stems of Gomphocarpus physocarpus: Distribution, structure and chemical composition

Gomphocarpus physocarpus (E. Mey.), commonly known as balloon milkweed and umbababa, is a short shrub of the Apocynaceae family native to southern Africa. In South Africa, all parts of the plant are used in traditional medicine to produce ointments for the treatment of warts, and the seeds are used in indigenous rituals. The leaves and stems produce a milky latex that is toxic, yet it has never been described in detail, particularly with regards to the anatomy of lactiferous cells. The present study was undertaken to examine the distribution and structure of the laticifers and the chemical composition of the secretions in the leaves and stems of G. physocarpus. Histochemical methods and light microscopy were used. The laticifers in the leaves were associated with the vascular system of the midrib and the larger lateral veins. Stem longitudinal and cross sections stained with safranin and fast green revealed the presence of laticifers in the pith, cortex and external to the phloem. Laticifers in the stems were branched, non-articulated and parallel to the longitudinal axis. The main compounds accumulated in the laticifers were phenols and alkaloids. Phytochemical screening of leaf and stem crude ethanolic extracts displayed positive reactions for the presence of carbohydrates, cardiac glycosides, steroids/terpenoids, alkaloids and phenols. The compound groups identified could potentially be contributing to the toxic nature of this plant. The biological and medicinal applications of G. physocarpus are yet to be assessed; therefore this study provides a foundation for future work. In addition, the knowledge of laticifer systems of G. physocarpus could be of taxonomic importance, considering that this study is the first on laticifers in this genus.